A sample assembly includes a stack of a sample and a hydrophobic elastic layer located on the back side surface thereof or a filter layer. The sample may include a biological material or a chemical, and can include an absorptive material. The filter layer includes an absorptive material in which a sample material is embedded. A sealing surface sampling probe including a knife edge lands on an area of interest in the sample or the filter layer. The hydrophobic elastic layer or the substrate in conjunction with the knife edge provides a complete sealing of a confined portion of the sample or the filter layer to prevent inclusion of any other material from outside the confined volume and to enhance the precision and sensitivity of the analysis.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made with government support under Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of Energy. The government has certain rights in this invention.